This article examines the governance of Islamic finance in two non-Muslim-majority sites of its expansion, the United States and the United Kingdom. An alternative form of economic rationality is being constructed and practiced across diverse sociospatial contexts to produce what we term cosmopolitan financial geographies. Building from recent debates about territoriality, embeddedness, and relationality in economic geography, we respond to calls for a more complex treatment of agency, developing the concept of cosmopolitan legalities to capture the dynamic multiterritorial, relational governance of Islamic banking and finance (IBF) that melds Western and Islamic financial rules and practices through the embodied religious authority of Shari'a scholars. These complex legalities demonstrate the significance of postcolonial and religious sociospatial contexts in the formation of financial markets suggestive of an evolving postcolonial political economy of “south-driven” alliances in a financial landscape dominated by neoliberal rationalities and subjectivities. The development of IBF has at the same time prompted regulatory shifts in the United States and United Kingdom, demonstrating the ongoing coconstitution of Islamic and interest-based financial markets.